Thermal sensing pressure switch



May 26, 1970 J. K. GARRETT THERMAL SENSING PRESSURE SWITCH Filed Nov.28, 1967 s: s- Ev Q; I 3 42 ;E r 5 30 did/5 A. 6416957 7' 1 INVENT'OR.7%

United States Patent 3,514,734 THERMAL SENSING PRESSURE SWITCH James K.Garrett, Inkster, Mich., assignor, by mesne assignments, to the UnitedStates of America as represented by the Secretary of the Army Filed Nov.28, 1967, Ser. No. 686,153 Int. Cl. H0111 37/40 US. Cl. 337320 3 ClaimsABSTRACT OF THE DISCLOSURE A thermo-sensing pressure switch for sensingair temperature in an engine compartment having a chamber which expandsand responds to increased temperature thereby causing a diaphragm toflex against a piston which is slidably mounted in the switch housing. Apiston which is biased against the diaphragm is caused to move so as tocontact a micro-switch mounted within the switch housing therebycompleting an electrical circuit and energizing a warning light in thedrivers compartment.

This invention relates to a thermo-sensing pressure Switch. Moreparticularly, this invention relates to a switch which is actuated inresponse to thermal conditions in internal combustion enginecompartments. Thermally responsive switches have been known in the priorart, however, these switches were not compact and the response was notsufficiently predictable under any given environment. Prior art sensingswitches were of a snap action type which were fast acting type inresponse to a relatively small change in temperature once a plateautemperature was reached. The present switch provides for a smoothoperating switch which can operate in a relatively warm environment.Prior art devices have a limited range and have relatively highresponse. The present invention provides for a switch which can operatein a relatively high temperature while still requiring a relativelylarge change in temperature to energize or deenergize a switch.

The present invention, therefore, provides for a thermal sensingpressure switch having a two piece housing, diaphragm, piston, spring,and a micro-switch. Ambient air at some initial pressure is trapped in asensing cavity formed in the housing. This pressure creates a force onthe effective area of the diaphragm which is counteracted by the forceof the spring. As the air temperature rises, the pressure within thesensing cavity also rises. This results in an increased load on thediaphragm. When this load exceeds the force of the spring, motion of thepiston and diaphragm occurs. At some increased pressure, piston contactis made with the micro-switch resulting in closure of an electricalcircuit.

It is, accordingly, an object of the present invention to overcome theabove mentioned defects in prior art warning systems for overheatedengine compartments.

It is another object of the present invention to provide a thermalsensing pressure switch for sensing air temperature in enginecompartments.

It is yet another object of the present invention to provide a thermalsensing pressure switch which is utilized to provide a monitor signalresponsive to an increase in temperature in the engine compartment.

It is yet another object of the present invention to provide a thermalsensing pressure switch which is fully automatic and does not requirecrew member actuation.

Other objects and advantages of the present invention will becomeapparent to those of ordinary skill in the art by the followingdescription when considered in relation to the accompanying drawing ofwhich the sole figure is a cross-sectional view of the switch accordingto the invention.

Referring now to the drawing, the main casing for the switch isindicated at 10 having flanges 30 extending about the lower edge.Diaphragm 26 is mounted on a receptacle 12 and clamped between flange 32of receptacle 12 and flange 30 of casing 10. A retainer 14 having a bore18 extending therethrough is conveniently located within casing 10.Flange 16 is provided on one end of retainer 14 in abutting relationwith shoulder 20' which is former in casing 10. A snap ring 24 securesflange 16 against shoulder 20 and prevents movement of the retainer 14.

Diaphragm 26 is formed of an elastomer and has a U-shaped told as shownat 28 secured therein. This fold permits pressure to increase on onlyone side of the diaphragm. Utilization of the U-shaped fold alsoeliminates the necessity of a seal between the piston 38 and the bore ofcasing 10. The disadvantage of using a seal is in thelfact that excessfriction is created by the use of such sea s.

A spring 44 is located about retainer 14 and is located between flange16 and the bottom 39 of piston 38. Piston 38 has side walls 37 which areslidably engaged with the internal bore of casing 10. The tendency ofthe spring 44 is to force piston head 39 downwardly and cause diaphragm26 to move towards receptacle 12. Mounted on the underside of diaphragm26 is a stop, indicated generally at 47 comprised of plate 34, bolt 48and nut 49. Plate 34 is held in engagement with diaphragm 26 to preventdownward movement thereof by spring 44. As can be seen in the drawing,flanges 36 are provided about the outer circumference of plate 34 toprovide adequate support for the diaphragm 26. Bolt 48 passes throughdiaphragm 26 and is secured to piston head 39. Hence, piston head 39,diaphragm 26, nut 49, and bolt 48 move as a unit. If desired the bolt 48and nut 49 may be adjustable so that plate 34 will permit increasedmovement of piston 38 in a downward direction.

The assemblage of parts including casing 10, diaphragm 26 and receptacle12 has thus provided a sensing cavity 40. Air is trapped within thesensing cavity 40 which will expand or contract in response to theenvironmental temperature in which the pressure switch is located. Ifthe environmental temperature increases, the air which is trapped withincavity 40 will expand, thus causing diaphragm 26 to flex upwardly. Ifhowever, the environmental temperature decreases, the diaphragm 26 willflex downward causing plate 34 and stop 47 to move downward until bolt48 engages receptacle 12. The tension of the spring 44 may be adjustedsuch that the pressure of the entrapped gas within cavity 40 will besuflicient to overcome the force of spring 44 at some predeterminedpoint.

Mounted within retainer 14 is a micro-switch which is shownschematically at 50. Leads 54 connect switch 50 in an electrical circuitcontaining an indicating light 56. At least one movable contact 52 isprovided at the bottom of the micro-switch 50 which when depressed willengage another contact within switch 50 and thereby complete theelectrical circuit in which the switch is located. Upon depression ofcontact 52, switch 50 will close thus completing the circuit andenabling power to flow thru leads 54 to the indicating light 56,thereby, indicating a desired sensed condition. The movement of thepiston 38 is designed to actuate switch 50 which is supported inretainer 40.

As can be seen in the drawing relief ports 46 are provided in casing topermit escape of air entrapped in chamber 42. As piston 38 is caused tomove upward against the force of spring 44, air will escape throughports 46 and thereby allowing diaphragm 26 to flex in an upwarddirection. If ports 46 were not so provided, the pressure of the airentrapped in sensing cavity 40 and chamber 42 on opposite sides ofdiaphragm 26 would tend to equalize in response to relatively identicalenvironmental conditions. This would seriously limit the eflicacy of thesensing switch.

If desired, a mechanical fuse could be utilized in place of bolt 48, andnut 49. These types of fuses are known in the art and provide amechanical force which would prevent movement of plate 34 and diaphragm26 in an upward direction until the fuse is broken. These type of fusescommonly break when a predetermined temperature is reached, therebymelting the fuse link and permitting movement of the diaphragm. Thisfeature would permit the present invention to incorporate the featuresof a snap action switch in addition to those features previouslymentioned. The use of a fuse of this type, however, has the disadvantagethat once the fuse is broken the support from plate 34 will beeliminated. If the switch is to be used in an environment where thetemperature is at a relatively high base and/or if the temperature tendsto fluctuate around the base reference temperature, this would cause thefuse to break and hence the use of such a fuse would be inadvisable.

In operation, the pressure switch is placed in an engine compartment forsensing air temperature and is mechanically fastened therein by anysuitable manner. The spring member 44 is so adjusted that the resultantpressure exerted on piston 38 will normally retain stop member 47 incontact with receptacle 12 and thus the electrical circuit will bede-energized and the indicating light 56 in the crew compartment will beoff. As the temperature within the engine compartment rises, thepressure of the air trapped within sensing cavity 40 increases. Whenpressure within sensing cavity 40 increases beyond a prede terminedthreshold pressure, piston 38 will slide upward against the force ofspring 44 until piston head 39 depresses contact 52. As piston 38 slidesupward, air entrapped in chamber 42 will escape through ports 46,thereby reducing the pressure on the upward side of the diaphragm 26.When contact 52 is depressed, micro-switch 50 will be closed, thereforethe electrical circuit including the indicator light 56 will becompleted. This will permit power to flow through leads 54 from anysuitable source such as a vehicle battery to the indicator light. Thiswill notify the vehicle operator to take necessary remedial steps tocorrect the abnormal temperature condition.

When the environmental temperature within the engine compartmentdecreases, the pressure of the entrapped air within sensing cavity 40will decrease and thereby permit diaphragm 26 to regain its originalposition wherein stop member 47 will rest against receptacle 12. Piston38 will also be forced downward against diaphragm 26 by the force ofspring 44 pressing against piston head 39. When piston head 39 is thuslowered, micro-switch 50 will no longer be closed due to the removal offorce on contact 52. The indicator light will then be de-energized,thereby indicating normal temperature operation.

While the thermo sensing pressure-switch has been indicated to haveutility within an engine compartment, it will be evident that the switchwill be operative within any environment in which an indication ofchange in temperature is useful and desirable.

While the switch has been described as being utilized to actuate anindicator light, it should be noted that the switch may be used tocomplete any electrical circuit.

What has been described therefore is a thermally responsive pressureswitch which is compact, durable, and able to operate smoothly in an airenvironment which is both fluctuating and at a relatively high basetemperature. The invention therefore further provides for a thermosensing switch which has a range and response which is not known in theprior art. A switch according to the present invention has a response,which is sufficiently low to permit fluctuations in the environmentaltemperature without adversely affecting switch operation.

Since it is obvious that many changes and modifications can be made inthe above described details without departing from the nature and spiritof the invention, it is to be understood that the invention is notlimited to said details except as set forth in the appended claims.

What I claim is:

1. A thermal sensing pressure switch comprising:

a casing having at least one movable contact forming a portion of aswitch mounted therein and an internal bore;

a receptacle shaped so as to form a sensing cavity;

a diaphragm clamped between said casing and said receptacle;

a piston slideably mounted in and engaging said internal bore so thatwhen the pressure increases in said cavity in response to increasedenvironmental temperature, said switch is activated; and

at least one fixed contact located within a micro-switch;

said micro-switch secured in a retainer which is fixed in said housingand extends into said piston.

2. A thermal sensing switch in accordance with claim 1 wherein:

said diaphragm has a U-shaped fold positioned therein extendingintermediate said piston and said casing so as to permit the diaphragmto flex toward said contact; and

a spring is mounted intermediate a portion of said retainer in saidpiston to bias said piston against said diaphragm.

3. A thermal sensing pressure switch comprising,

a casing,

a receptacle,

a diaphragm,

a piston,

a retainer,

a micro-switch,

a spring biasing means,

and a support means,

said diaphragm being clamped between said casing and said receptacle soas to form a sensing activity and an exhaust chamber,

said support means comprising a plate mounted within said sensing cavityand attached to said piston,

said retainer being mounted within said casing so as to form saidexhaust chamber intermediate said retainer and said piston,

said piston having a piston head which is in engagement with saiddiaphragm and a side member which is slidably engaged with said casing,

said micro-switch being mounted within said retainer and having at leastone movable contact,

said spring means being mounted intermediate said retainer and saidpiston whereby the pressure of gas which is trapped within said sensingcavity will inand cause said diaphragm to flex against said piston so asto permit said piston to slide and cause said piston head to engage saidcontact of said micro- 5 6 switch when the environmental temperaturereaches 2,688,064 8/ 1954 Traver 337320 a predetermined thresholdtemperature. 3,324,262 6/ 1967 Noth 337-320 References Cited FOREIGNPATENTS 198,367 5/1923 Great Britain.

UNITED STATES PATENTS y 6t -1 *?2 BERNARD A. GILHEANY, Primary Examinergf g g f 333:; DEWI'IT M. MORGAN, Assistant Examiner Starbird 337-315Szwargulski 200-835 10 Mayo 337 320 20083.5, 83.91; 337-327 Coffin337320

